A touch panel as a device of sensing a touch input of a user on a display device has been widely used in display device in public facilities and in large display devices such as a smart TV in addition to personal portable devices such as a smart phone and a tablet PC.
Recently, in order to decrease the thickness of the display device and improve visibility, an in-cell type touch panel integrated display device in which the touch panel is integrated to the display device has been developed. Generally, the touch panel includes a transparent touch electrode made of transparent conductive oxide (TCO). Although the transparent touch electrode improves visibility of the touch panel integrated display device, it has high resistance, and thus, an RC-delay of the touch panel is increased. In order to solve the problem, a touch panel having a metal mesh structure including a line electrode with a mesh pattern has been developed.
FIG. 1 is a schematic plan view for describing a touch panel having a metal mesh structure in the related art. FIG. 2 is a schematic cross-sectional view for IIa-IIa′ and IIb-IIb′ of FIG. 1. Referring to FIGS. 1 and 2, a touch panel 100 having a metal mesh structure in the related art includes a substrate 110, a first line electrode 120, a second line electrode 130, a routing line 150, and a pad 160. The first line electrode 120 and the second line electrode 130 are extended in different directions, and the second line electrodes 130 are separated from each other in a cross area. The first line electrode 120 passes between the separated second line electrodes 130, and the separated second line electrodes 130 are connected with each other by a connection electrode 140 in the cross area. As a result, the first line electrode 120 and the second line electrode 130 may cross each other while being electrically separated from each other.
The first line electrode 120, the second line electrode 130, the routing line 150, and the pad 160 are disposed on the same layer on the substrate 110 and made of a metal such as copper (Cu). However, since copper (Cu) is oxidized well, a passivation layer 172 made of an inorganic material is disposed on the first line electrode 120, the second line electrode 130, the routing line 150, and the pad 160. On the passivation layer 171, an over-coating layer 172 for electrically separating the first line electrode 120 and the connection electrode 140 from each other and planarizing an upper surface of the touch panel 100 is disposed. In order to connect the separate second line electrodes 130 with the connection electrode 140 in the cross area, contact holes may be formed in the over-coating layer 172 and the passivation layer 171, respectively. The contact hole of the over-coating layer 172 is formed by development and the contact hole of the passivation layer 171 is formed by a dry etching process. However, since it is difficult to control an etching degree by the dry etching process, the passivation layer 171 may be more internally etched than the side surface of the over-coating layer 172. Accordingly, as illustrated in FIG. 2, in the process of forming the contact holes, an undercut structure DP in which the passivation layer 172 is recessed inside the over-coating layer 172 is frequently generated. The connection electrode 140 is formed on the over-coating layer 172 by a deposition process, and the connection electrodes 140 are disconnected from each other by the undercut structure DP. As a result, the second line electrode 130 and the connection electrode 140 are not connected with each other.
Meanwhile, when the contact holes are formed in the over-coating layer 172 and the passivation layer 171, an opening OA exposing the pad 160 may be simultaneously formed. After the opening OA is formed, the connection electrode 140 is patterned. Further, in a process of etching the connection electrode 140, the pad 160 is often damaged by an etchant for etching the connection electrode 140.